Apparatus for checking of travelling yarn in textile machinery



July 5, 1966 w. GITH 3,258,824

APPARATUS FOR CHECKING 0F TRAVELLING YARN IN TEXTILE MACHINERY Filed Sept. 25, 1964 5 Sheets-Sheet 1 Lu 3 2 '3 a U k u b Q.

I! BE '1 2 U W. GlTH July 5, 1966 APPARATUS FOR CHECKING 0F TRAVELLING YARN IN TEXTILE MACHINERY Filed Sept. 23, 1964 5 Sheets-Sheet 5 X U L 0 0 5 A w 3 a W m w L M H s o 0 3 Quiz 0 G 0 0N 2 T m .V V/V v MM 5 I m 22% n... m w. m. m F||I N wbqvx MWQN 1.||| M5408 mm m FIG. 4

INVA'NTOA" W. GlTH July 5, 1966 APPARATUS FOR CHECKING OF TRAVELLING YARN IN TEXTILE MACHINERY Filed Sept. 23, 1964 5 Sheets-Sheet 4 lNVENTOI? July 5, 1966 w. GlTH 3,258,8

APPARATUS FOR CHECKING 0F TRAVELLING YARN IN TEXTILE MACHINERY Filed Sept. 23, 1964 5 Sheets-Sheet 5 TE g b S g I 1 c INVENI'OP MAM W United States Patent Claims. E01. 2864) My invention relates to apparatus for checking travelling yarn in textile machine for slubs, doubling or the like I faults.

The yarn being processed in a textile fabricating machine, for example wound to a yarn package in a winding machine, must be supervised for detecting the occurrence of slubs, or such faults as double or multiple threads as may result from knotting operations. It has been proposed to employ for such purposes a measuring device which superimposes upon an electrical base voltage a fault-responsive pulse for releasing a protective device which prevents the further processing of the faulty yarn. The base parameter value upon which the electrical pulses are superimposed, may also be constituted by the electrical intensity, frequency or other parameter. The base value itself may possess any magnitude and hence may also be equal to zero, for example, in which case the faultresponsive measuring or sensing device is merely required to produce pulses. However, the base value may also have a magnitude departing from zero so that, for example, during normal yarn-processing operation, a constant output value is furnished from the sensing or measuring device and the occurrence of slubs, multiple threads or the like results in the superposition of larger or smaller measuring pulses upon the normally constant base value of the output, these signals then being employed for releasing the above-mentioned protective device which prevents the further processing of the yarn.

In apparatus of the above-mentioned type, as heretofore known, the supervision of the travelling yarn is effected in such a manner that differences in cross section, diameter, or volume of the yarn as are caused by a slub or by multiple threads are sensed by a measuring member, and the measuring value corresponding to the change in yarn dimension is amplified through a differentiating circuit before being supplied to the protector device, such as a device which severs the yarn. In the operation of these measuring devices, which are designed as yarn cleaners, the ever-increasing demands for greater precision have increasingly manifested an appreciable lack in desired selectivity. This shortcoming resides in the fact that there is a relatively wide range of uncertainty within which the apparatus may or may not become effective to prevent the processing of faulty yarn. That is, there is no definite line of separation beyond which all slubs or equivalent faults are eliminated but rather there is a wide band of stray. It happens that slubs above the desired limit are not detected but, on the other hand, slubs below the desired limit are detected and cut out of the yarn. The reason for this uncertainty is the fact that, due to the differentiating operation in the known equipment, the measuring result is dependent upon time, because the control pulse supplied to the yarn severing device is dependent upon the dimensional change of the yarn per unit time and consequently upon the shape of the slub.

It is an object of my invention to provide a. yarn checking apparatus for the above-mentioned purposes which is free of such shortcomings and affords a much more precise selectivity with respect to the prevention of processing involving unsuitable yarn. The invention is based upon the recognition that a satisfactory checking of travelling yarn on the basis of the differentiation is not feasible,

3,258,824 Patented July 5, 1966 but that only a difference measurement can furnish unambiguous results. This will be explained with reference to FIG. 1 of the accompanying drawings.

Shown at a, b, c, d and e in FIG. 1 are respectively different shapes of a slub in a thread of yarn (shown schematically). The graph immediately below the schematic representation of the slubs shows the transverse cross-sectional dimension (on the ordinate) versus the length (on the abscissa) of the slub. The illustrated slubs and cross sections are so chosen that all of the slubs have the same maximum cross-sectional dimension. The third graph in FIG.1 shows the voltages on the ordinate (versus length on the abscissa) obtained by differentiation and hence, the corresponding rate of change, with reference to the cross-sectional graphs shown above the respective voltage diagrams.

Since the voltage curves obtained by differentiation are dependent upon the flank steepness, it is apparent from FIG. 1 that in cases a, b and 0 very high output pulses are obtained, but that the output voltages resulting from the slubs a' and e are considerably lower. Since all possible slubs are not to be eliminated but only those which exceed a given cross-sectional diameter, a selection must be made between the voltage pulses represented by the bottom graph in FIG. 1 so that the yarn severing device is released only if the output voltage corresponds to a slub cross-sectional dimension beyond a permissible maximum.

If one places the limit of selector sensitivity, for example, at the level of the dot-and-dash lines 1 and g, it will be recognized that the slubs a, b and c are eliminated, but that the slubs d and e are not detected or eliminated, despite the fact that the slubs d and e, on account of their large cross section, should also have been eliminated.

It is therefore another object of my invention to improve the selectivity of yarn supervisory apparatus in such a manner that it will reliably respond to a predetermined maximum limit with respect to the diameter, cross section or volume of a slub or equivalent fault of the travelling yarn, regardless of whether the slub possesses a steeper or more gradually curved shape.

As mentioned above, this result is achieved by substituting the known differentiating method by a genuine difference measurement. As a consequence, all departures of the cross-sectional dimension located above a given limit, such as the one indicated by the line h in the second diagram of FIG. 1 are reliably detected and made effective for releasing the severing device. It will be recognized that a difference measurement, using a limit such as the line h as a criterion, will result in eliminating all of the illustrated slubs a to e irrespective of their particular shape.

According to my invention, this result is achieved by providing the yarn checking apparatus with a yarn sensing transducer which issues electrical signal pulses in response to the slubs and other faults to be detected, and with a direct-current amplifier in the input circuit of which the signal pulses are superimposed upon a fundamental operating voltage, while the output circuit of the amplifier is connected with an electrically actuable device for stopping the yarn processing operation in response to the signal pulses. Furthermore, the amplifier is provided with regulating circuit means, preferably a negative feedback circuit which maintains the voltage of the amplifier output circuit substantially constant relative to changes of the fundamental component of the input voltage, so that the controlled device is actuated only in response to the yarn-fault signals independently of changes in fundamental voltage. The device for stopping the yarn processing operation may serve to block the winding operation of a winding machine for example, or it may prevent the knotter of such a Winding machine from performing the knotting operation. The device may also effect severing of the yarn by tearing or cutting it, or it may serve to block the further travel of the yarn by arresting it.

It will be understood that, in lieu of the conventional alternating current amplifiers equipped with differentiating R-C members, the apparatus according to the invention requires the provision of a direct-current amplifier which forms a genuine difference with respect to the cross section, diameter or volume of the yarn. Such a difference formation is independent of shape as well as time. Consequently, an apparatus according to the invention is suitable for operation with different travelling speeds of the yarn. In differentiating measuring equipment, due to the fact that the measurement or the change in cross section is dependent on time, the difficulty of providing definite measuring or sensing results arises even in the cases during operation when the yarn travel speed is only very slight. For example, it has been virtually infeasible with the conventional differentiating equipment to obtain satisfactory results during the starting-up period of a winding station. In contrast thereto, an apparatus according to the present invention secures satisfactory checking results not only during the gradual acceleration of a winding station up to its normal operating speed, but also permits a sensing operation with the yarn at standstill.

A direct-current amplifier to be employed for difference formation in apparatus according to the invention, however, generally exhibits the disadvantage that it uniformly amplifies not only the signal pulses superimposed upon the base or fundamental voltage or input current, but also any fluctuations or changes of the input fundamental parameter. Such fluctuations may occur, for example, as a result of fluctuations in feeder voltage or due to changes in temperature. If the sensing member which produces the fault-responsive signal pulses consists of a photoelectric cell, different illumination intensities, stemming for example from different brightness of the light sources employed for illuminating the photoelectric cells, may also have the effect of changing the normal input value of the voltage or current supplied to the input circuit of the amplifier. If the electrical signal pulses are produced with the aid of a capacitive sensing device such as a capacitor, then slight changes in the humidity content of the yarn or of the ambient air may cause changes in the fundamental input parameter value of the amplifier.

It is therefore another object of the invention to eliminate such disturbing effects due to changes in normal input voltage or current upon which the signal pulses from the sensor are superimposed; and this is achieved by employing a direct-current amplifier whose output voltage or current is regulated for constancy relative to any changes in input voltage or current. As mentioned, this is achieved by providing a feedback between the output circuit of the amplifier and the input circuit in which the sensor is connected. The desired independence of the amplifier output voltage from changes in fundamental input voltage is then achieved, according to a more specific feature of the invention by connecting to the fundamental input value, or a proportional share thereof, a seriesopposed voltage derived by feedback from the output circuit of the amplifier and proportional to the amplifier output voltage.

According to still another feature of the invention, a feedback regulation is preferably effected in such a manner that only a portion of the amplifier output voltage which is above an adjustable limit value, is series opposed to the voltage proportional to the fundamental input voltage. For determining the adjustable magnitude of the desired limit, a Zener diode is connected into the feedback circuit for example. As is well known in the electronics arts, a Zener diode acts as a voltage limiter or regulator. For a detailed description of its characteristics, reference can be had, for example, to Silicon Zener Diode and Rectifier Handbook complied by the Applications Engineering Department of the Semiconductor Products Division of Motorola, Inc.

The invention will be further described with reference to the accompanying drawings, in which:

FIG. 1 shows the group of explanatory diagrams discussed in the foregoing.

FIG. 2 is a schematic circuit diagram of an apparatus embodying the invention by way of example.

FIG. 2a shows a sensor and severing device applicable in the apparatus according to FIG. 2.

FIG. 2b shows a modified embodiment of a sensor also applicable in an apparatus otherwise corresponding to FIG. 2.

FIG. 3 is an explanatory graph relating to the performance of apparatus according to FIG. 2.

FIG. 4 is a circuit diagram of a bridge-typenetwork of two cooperating sensors applicable in apparatus otherwise corresponding to FIG. 2.

FIG. 5 shows the circuit diagram of the modified severing device applicable in apparatus according to FIG. 2.

FIG. 6 is a schematic circuit diagram of another apparatus also embodying the invention.

FIG. 7 illustrates schematically a further embodiment of apparatus according to the invention; and

FIG. 8 is an explanatory diagram relating to the apparatus according to FIG. 7.

Referring to FIGS. 2 and 2a, the illustrated apparatus comprises a sensing device whose sensor 101 consists of a photoelectric cell, such as a silicon diode, which generates a voltage in dependence upon the amount of illumination issuing from a light source 101'. The yarn Y travelling upwardly from a supply coil or a knotter to a take-up spool, passes through the sensing gap of the device, so as to throw a shadow image upon the active surface of the cell 101. As long as the cross section of the travelling yarn remains constant along its length, the generated voltage of the photocell 101 remains constant, but when the yarn has a slub or other cross-sectional irregularity, the shadow travelling over the cell surface varies accordingly so that the generated voltage likewise changes.

The apparatus is further provided with a severing device which, in the embodiment according to FIG. 2a, comprises a normally inactive cutter which, when actuated by an electromagnet 100, will cut the yarn. A photocell 101 is connected at its terminals L, K in a potentiometer circuit as shown in FIG. 2, so that the volt-age generated in the cell 101 varies in response to the passage of a slub. The resulting voltage pulses are amplified in a direct-current amplifier which energizes the magnet 100 and thus operates the cutter 100.

While in FIG. 2 the cutter magnet 100 is shown connected directly in the output circuit of the illustrated amplifier, it will be understood that a control relay may be interposed between the amplifier output circuit and the actuating cutter magnet.

In the embodiment according to FIG. 2, the amplifier comprises four amplifying stages with respective transistors 10 2, 103, 104-, and a regulating stage with a transistor 106.

The transistor 102 operates in grounded emitter configuration and thus has a high input resistance. The next following stages 103 to 105 are galvanically coupled in cascade. All transistors 102 to 106 are connected between the negative terminal A and the positive terminal B of a direct-voltage source, the positive terminal B being grounded. The cutter control magnet or relay 100 is series connected in the collector circuit of the transistor 105 in the output stage. This output circuit also comprises a series-connected diode 109 which serves as a threshold member and thus imparts to the amplifier stage of transistor 105 a corresponding switching characteristic. Similar threshold valves 107 and 108 are connected in the emitter circuits of the respective transistors 103 and 104, the diode 108 for transistor 104 being additionally operative with respect to the transistor 105.

The transistors 103, 104 and 105 have a common adjustable emitter resistor 110 which has a very low-ohmic value in comparison with the other resistors. By virtue of the negative feedback coupling still to be described, the resistor 110 permits controlling the amplifying gain or sensitivity of the amplifier. The collector circuits of transistors 102, 103 and 104 contain respective resistors 111, 112 and 113. In analogy to the gain-control resistor 110, a resistor 114 is connected in the emitter circuit 102 and an adjustable potentiometer rheostat 115 is connected in the emitter circuit of transistor 106.

When the photocell 101 is shaded by the passage of a slub, a double yarn or the like, the change in output signal causes the transistor 102 to be turned on in a manner more fully described hereinafter. Thus, a current will now flow from negative terminal A through the resistor 111, transistor 102 and resistor 114 to the positive terminal B. Due to this current flow, the negative potential at the point E in the emitter circuit of transistor 102 is raised to a potential determined by the resistance magnitudes of resistances 111 and 114, with the result of turning the transistor 103 on. Now a current will flow from terminal A through resistor 112, transistor 103, threshold diode 106 and resistor 110 to terminal B. A circuit point F between transistors 103 and 104 which, as long as transistor 103 is turned 011, has approximately the same negative potential as the terminal A, now assumes, due to the conducting condition of transistor 103, a more positive potential which nearly corresponds to that of the negative terminal B. This has the effect of blocking the transistor 104. Consequently, the current which, when transistor 104 is turned on, will flow from terminal A through resistor 113, point G, transistor 104, threshold diode 108 and resistor 110 to terminal B, is now interrupted. This causes the negative potential at point G to be raised considerably so that the transistor 105 is turned on and passes current through the cutter coil 100. To the extent described so far, the amplifier circuit is known per se.

However, according to a feature essential to the invention, the voltage normally occurring at the collector point D of transistor 105 and corresponding to the output voltage of the amplifier, is kept constant even if the fundamental or base voltage which is impressed across the input terminals K, L and which determines the working or zero point of the amplifier, should change. It should be understood, that the voltage at point D is to be constant only with respect to changes of the input fundamental voltage, but not with respect to the signal pulses which result from slubs and other yarn faults and which are superimposed upon the voltage across the input terminals K, L. As mentioned, the changes in fundamental input voltage may stem from changes in temperature or other effects acting upon the amplifier as well as upon gradual changes in brightness of the illumination produced by the light source 101' (FIG. 2) or also by the obscuring of the photocell 101 due to the gradual deposition of dust thereon. Any such changes in fundamental input voltage differ from the superimposed signal pulses in that changes of the fundamental voltage occur at a relatively slow rate.

The constancy of the amplifier output voltage at point D with respect to such slow changes in fundamental input voltage between the terminals K, L is achieved by virtue of a regulating feedback circuit which commences at point D between the cutter control coil 100 and the transistor 105. This feedback circuit has the purpose of furnishing a voltage proportional to the output voltage at point D, and placing this feedback voltage in bucking relation to the fundamental input voltage impressed in the input terminals K, L. It is particularly advantageous if the entire voltage proportional to the output voltage at point D is not thus applied in opposition to the fundamental input voltage, but if only a share of the output voltage at point D is thus applied, this share having a value above an adjusted limit magnitude. For determining such an adjustable limit magnitude, the feedback circuit is provided with a Zener diode 116. It is further preferable if the above-mentioned share of voltage, having a value above the limit determined by the Zener diode 116, is supplied in series-opposition to the fundamental input voltage through an electrical storage component, this component being constituted by a capacitor 118 in the illustrated embodiment. To secure a time constant of sufiicient length without requiring the capacitor 118 to be of excessively large dimensions, the regulating feedback voltage is preferably applied to the input circuit of the amplifier through an auxiliary amplifying stage constituted by the above-mentioned transistor 106 and the potentiometer rheostat 115.

In order to explain the functioning of the regulating feedback, reference will be made in the following toan arbitrary selection of numerical parametric values, it being understood that many other possibilities are available.

We shall assume that a voltage of 20 volts is applied between the terminals A and B, the terminal B having zero potential and the terminal A a potential of minus 20 volts. Due to leakage currents or the like, a slight amount of current will normally fiow through the cutter control coil so that the potential at point D is minus 18 volts for example. This voltage of minus 18 volts is reduced by the Zener diode 116 by a constant value, for example of about 15 volts, so that normally the point H of the feedback circuit will have a residual potential of about minus 3 volts. This residual voltage charges the capacitor 118 through the resistor 117. Simultaneously a control current flows through the base-emitter path of the transistor I106 and the rheostat 115. The transistor 106, like the transistor 102, is operated in grounded emitter configuration so that it also possesses a high input resistance. Furthermore the auxiliary amplifier stage of transistor 106 constitutes an impedance matching transformer because the load resistance of rheostat 115 in the emitter circuit of transistor 106 is low ohmic.

Depending upon the magnitude of the voltage at point H, the transistor 2106 conducts more or less current from terminal A through the collector and emitter of transistor 106 and through the rheostat 115 to the terminal B. This current produces in rheostat 115 a voltage drop of which a portion is tapped off and is connected in seriesopposed relation to the voltage of the photocell 101 at input terminal K. As will be explained hereinafter, the negative voltage tapped ofi the rheostate 1'15 always adjust itself automatically so that the above-presumed voltage of minus 18 volts at point D remains preserved.

Now assume, for example, that the voltage of the photoelement 101 slowly decreases due to the deposition of dust. Then the base of transistor 102 receives a more negative bias voltage, and this transistor then permits a higher current to pass through the resistors 111 and 114. This also increases the current passing through the transistor 103, which in turn reduces the forward current passing through the transistor 104, so that the current passing through transistor 105 is increased. This effects a gradual reduction of the voltage at point D. Consequently a slowly increasing shading of or drop in illumination at the sensor cell 101 causes a corresponding gradual decline of the voltage at point D. Since the Zener diode 1-16 always enfonces a constant voltage drop, a decline of the voltage at point D from minus 18 volts to minus 17 volts, for example, has the effect of reducing the voltage at point H from minus 3 to minus 2 volts. The reduced voltage of point H causes a reduced control current to flow through the emitter of the transistor 106 so that voltage drop of the rheostat also becomes lower. The correspondingly lower feedback voltage at input terminal K is now in series opposition to the lower voltage of the slightly darkened cell 101. The

regulating feedback is so rated that the voltage at input terminal K is reduced by the same amount by which the voltage of the photocell 101 has been increased. Consequently, the transistor 102 is controlled for the same state of conductance as existed prior to the occurrence of the slight shading of the cell 101, so that the other transistors 103, 104, 105 also operate under the original control conditions, and the point D is regulated to the original value of minus 18 volts.

The above described, very effective regulating feedback comp-rising the Zener diode 116 operates with delay due to the capacitor 118. The delaying time can be adapted to the requirements of the particular application by employing a capacitor 118 of corresponding capacitance value.

In the embodiment shown in FIG. 2, the operating voltage of the first amplifier stage comprising the transistor 102 is stabilized by another Zener diode 1 19. Regardless of the state of conductance of transistor 102, i.e. irrespective of the amount of current passing through the resistor 111, the point M in the collector circuit of transistor 102 is always maintained at a predetermined maximum voltage, for example minus volts. If this voltage, for example due to increased blocking of transistor 102, is increased to a higher value, then the excess voltage would be shunted off through the Zener diode 119.

The embodiment shown in FIG. 2 is further provided with two capacitors 120 and 121 which prevent the occurrence of high-frequency oscillations in the amplifier. A resistor 122 serves for determining the operating point of the threshold diodes 108 and 109. Provision is further made for interrupting the feedback circuit at R by means of a switch 130 so that the connection from resistor 117 to capacitor 118 and transistor 106, as well as the connection of capacitor 118 to transistor 106 is eliminated. When the switch 130 is opened, the capacitor 118 cannot be charged, nor can the capacitor 118 discharge through the transistor 106. Furthermore, under these conditions, the transistor 106 cannot receive a regulating pulse from point D. The operation of switch 130 is important for immediately regaining the original regulating condition of the direct-current amplifier in the event of yarn interruption.

According to the foregoing description, the embodiment shown in FIG. 2 is provided with a sensing member constituted by a photoelectric cell which furnishes voltage pulses when responding to the passage of slubs, double threads or similar yarn faults. While this photocell is assumed to be of the voltage-generating type, it will be understood that it may also consist of a resistance diode which varies its ohmic resistance in accordance with changes in illumination. Such a photocell has normally a given resistance and is normally supplied with a given voltage so that the current passing through the cell produces a voltage drop which constitutes the above-mentioned fundamental input value of the amplifier, the cell resistance and consequently the output voltage being changed in response to the presence of slubs or other yarn faults so that the resulting changes in voltage drop are composed of the fundamental magnitude and a superimposed pulse voltage.

However, if desired, the fault-responsive sensor in the apparatus according to the invention may operate on a different principle. For example a capacitive sensing or measuring member may be used. Such an embodiment is illustrated in FIG. 2b. The yarn Y travels between the two electrode plates 90 and 91 of a capacitor which is connected in a bridge circuit 92 normally balanced to provide no output voltage, or a given constant output voltage through a rectifier 94 to the input terminals L, K of the amplifier. The passage of the slub or other yarn fault through the capacitive sensor unbalances the bridge network and thus causes a pulse voltage to be applied to terminals L, K.

I prefer, however, to provide one or more light-sensitive cells as sensing devices to the use of capacitive sensors because of the improved stability of operation afforded by photoelectric devices. As mentioned, the humidity content of the yarn and of the ambient air affects the measuring result when using a capacitive sensor. The dielectric constant of water is and that of textile threads is about 2 to 6. Consequently, even slight fluctuations in humidity have a considerable effect upon the result of capacitive measurements. For this reason, optical sensors are generally preferable. The disadvantages of optical measurements, such as the effect of dust collection and fluctuations in brightness due to unstable current supply, for example which are able to vary the fundamental input value and thereby the working or zero point of the amplifier, are compensated satisfactorily by the above-described regulating feedback circuit.

Particularly advantageous is the use of a silicon diode as light-sensitive cell. It is known that the short-circuit current of a silicon photodiode increases and decreases in linear proportion to the illumination. However, the noload voltage of a silicon diode does not vary linearly but rather logarithmically. This logarithmic behavior of the no-load voltage can be advantageously utilized in the performance of yarn-fault checking apparatus according to the invention. This will be explained with reference to FIG. 3.

The diagram shown in FIG. 3 indicates along the abscissa the amount of illumination in lux to which the active surface of the silicon photodiode is subjected, and the ordinate indicates the corresponding voltage. The curve represents the no-load voltage U in dependence upon the intensity of illumination. It will be recognized that, for example, a shading of 20% always results in the same voltage change U regardless of the absolute illumination intensity, except that only the base values of the voltage are different in dependence upon the illumination intensity. Since, as explained above, these different base values of voltage are compensated by the regulating feedback circuit in an apparatus according to the invention, these different base values have no effect upon the amplifying performance.

It is of great importance, however, when using a silicon photodiode that the amplifier according to FIG. 2 be controlled in accordance with another feature of the invention, in dependence upon the no-load voltage of the silicon diode. This is achieved by operating the first amplifier stage with the transistor 102 in common emitter configuration and thereby having a high input resistance. As a result, the silicon photodiode 101 is subjected almost to no-load current so that the no-load voltage of the diode 101 can become effective.

Regardless of whether the direct-current regulated amplifier, such as exemplified by the embodiment shown in FIG. 2, is photoelectrically or capacitively controlled in apparatus according to the invention, it is sometimes preferable to employ two sensors instead of only one in order, for example, to permit comparing the yarn dimensions at two mutually spaced localities simultaneously one with the other. Thus, FIG. 4 shows by way of example a sensor stage equipped with two silicon photodiodes 101a and 101b which are applicable, in lieu of the single photocell 101 (shown in FIG. 2), for controlling the direct-current regulated amplifier. The two photodiodes 101a and 101b according to FIG. 4 are connected in respective legs of a bridge network which is connected to the input terminals L and K of the amplifier shown in FIG. 2. As long as the two photocells are uniformly illuminated, that is for example as long as the cross section of the yarn portion shading the diode 101a is equal to the cross section shading the diode 101b, no voltage drop is produced at the diagonal resistor of the bridge network. However, when one of the two diodes is shaded less or more than the other, a current passes through the resistor 125, and the corresponding voltage drop is impressed across the input terminals K and L of the amplifier.

An adjustable potentiometer or rheostat 126, which forms two other legs of the bridge network permits calibrating the zero point of the network. Another adjustable rheostat 127 serves for adapting to one another the generally slightly different voltage characteristics of the two photodiodes according to FIG. 3, so that for the same amount of shading the same voltage drop is produced in both diodes.

A sensor device of the type shown in FIG. 4 is particularly advantageous for detecting double or multiple threads. For this purpose, the photodiodes 101a and 10112 are spaced from each other along the yarn path, and the respective voltage value simultaneously determined ahead of the knot and behind the knot are compared with each other in the bridge network. In the event a double thread is formed, the comparison shows a difference, causing the machine operation to stop, for example, by actuating the yarn cutter coil 100 through the operation of the amplifier shown in FIG. 2.

When the input stage of an amplifier as exemplified in FIG. 2 is controlled by a sensor device of the type shown in FIG. 4, the pulses supplied to the amplifier input terminals K and L may change their polarity. remembered that on the basis of the aforementioned numerical examples, the voltage impressed upon the cutter control coil 100 under normal operating conditions, that is when no fault-responsive pulses are applied to the input terminals K and L, amounts to only two volts because the coil 100 is connected between the minus 20 volts of terminal A and the regulated minus 18 volts at point D. If a pulse, instead of reducing the negative voltage would increase the negative voltage from minus 18 volts to minus 19 or minus 20 volts, for example, then the coil 100 could not properly respond.

It is therefore preferable, in cases where positive as well as negative input pulses are to be expected, to modify the control magnet 100 so that it will respond to an increase as well as decrease of the amplified output voltage. An embodiment of such a modification is shown in FIG. 5, it being understood that the circuit portion of FIG. 5 is applicable in a system otherwise corresponding to FIG. 2. The electromagnet 100a shown in FIG. 5, which either directly controls the yarn cutter as shown in FIG. 2a or constitutes part of a control relay for the cutter, is provided with two mutually opposed windings and 100a. The winding 1000 is connected between the voltage supply terminals A and B in series with an adjustable resistor 128. Thus, the constant voltage adjusted by means of the resis tor 128 can be impressed on the winding 1000. The winding 100b acting opposite thereto is connected in the output circuit of the amplifier according to FIG. 2. While the amplifier output circuit according to FIG. 5 is different from that shown in FIG. 2, it will be understood that such and other modifications are readily applicable. It will be recognized that according to FIG. 5 the winding 10% forms part of a voltage divider whose tap point D is the starting point of a regulating feedback circuit extending through the Zener diode 116 to the transistor 106 (FIG. 2). The transistor 105 in this case is so controlled that the voltage normally obtaining between points C and D--this voltage being,

for example, minus 10 volts as assumed in the foregoingis equal to the voltage between the points C and N of the second winding 1000 (FIG. 5). The mutually opposed magnetic fields of the respective windings 10017 and 1000 nullify each other so that the yarn cutter does not normally respond.

During slow changes of the fundamental input parameter, the potential of point D is regulated for constancy as in the embodiment according to FIG. 2. However, when a rapid positive or negative pulse issues from the photocells 101a and 1011) according to FIG. 4, for example due to the occurrence of a double thread, then the voltage at point D (FIG. 5 rises or drops, and the magnet 100a will respond because now one of the two magnetic fields will predominate.

It will be When a sensor device according to FIG. 4 is being used not only for detecting double threads but also for responding to slubs, for example as a yarn cleaner, it may be possible that a very short slub may be encountered. A short slub would produce a correspondingly short voltage pulse between terminals K and L, and such pulse may be shorter than the term of response required for the relay or magnet or 100a. In order to make certain that even the shortest pulses will suflice for energizing the magnet for a sufficient length of time, the last amplifier stage may be provided in the form of a monostable switching stage, for example.

When a device according to FIG. 4 is to be employed for detecting double threads, it is desirable that the magnet 100a (FIG. 5) be not energized by the pulse stemming from the passing of the knot through the sensing location, because otherwise the passing of each knot would result in the severing of the yarn even when no double thread were present. The very short pulses produced by the passage of the knot itself, therefore, are not supposed to cause a response of the cutter or cutter relay. Such performance can be achieved, for example, without requiring a multivibrator, simply by taking advantage of the pick-up delay of the cutter or cutter relay.

It has been mentioned hereinabove that an apparatus according to FIG. 2, modified by employing the bridgetype sensor according to FIG. 4 and the amplifier output circuit according to FIG. 5, is suitable for the purpose of detecting multiple threads by comparing the measuring or signal voltage from respective sensing operations simultaneously effected in the yarn portions preceding and following a knot respectively. However the measuring values ahead of a knot and behind the knot may also be determined sequentially, stored and then compared with each other in a bridge network. The storing of the two measuring values may be effected for example in two capacitors, and the very short voltage pulse produced by the knot itself may be used for releasing the switching from the first to the second capacitor. An electrical timing member may then discontinue the measuring operation and initiate the voltage comparison, which thereafter, in the event of a discrepancy, will release the pulse for controlling the yarn severing device. The voltage pulse produced by the knot may be given an increased amplitude 'by means of a resonance member so as to become ineffective with respect to the charging of the storage capacitors.

An embodiment of apparatus for response to multiple threads by comparing measuring values determined successively ahead of and behind a knot in the above-described manner, is shown schematically in FIG. 6. A sensing device for this apparatus comprises two photoelectric cells 101a and 101d. While these are shown only schematically, they are preferably so mounted that their respective sensitive surfaces are located at right angles to each other, the yarn to be checked passing through the intersection point of two beams of light impinging upon the respective cell surfaces. Such a photoelectric sensing device is more fully described and illustrated in the copending applications Serial No. 307,077, filed September 6, 1963, of H. Raasch and W. Gith and Serial No. 398,653, filed September 23, 1964, of H. Raasch. The two cells 1010 and 101d are parallel connected between the amplifier input terminals K and L. The apparatus would also be operative if only one photo cell were used, but in such a case the particular advantages of operating with intersecting light beams would be missmg,

The feedback regulated amplifier 129 controlled by the two silicon diodes 101a and 101d corresponds to the one shown in FIG. 2, so that it suffices to indicate in FIG. 6 only the amplifier terminals A, B, C, D, L and K. In the amplifier there is provided a start-control switch 130 which is closed manually or automatically whenever a knotting operation is terminated and the yarn commences its travelling motion. This is because the sensing operation is to commence only at this instant, since the yarn is already located in the sensing gap prior to the commencement of the yarn travel. The provision of the switch 136 also ensures that any pulses which may occur when the yarn is being inserted into the sensing gap will not cause the release of the cutter-control magnet 101) (FIG. 2). As shown in FIG. 2, the start-control switch opens the feedback circuit at point R. Since the capacitor 118 is capable of storing its voltage during greatly prolonged periods of time, the closing of switch 13-0 immediately causes the voltage of capacitor 118, acting upon the transistor 1% and the potentiometer rheostat 115, to promptly reestablish the regulating condition existing prior to the preceding opening of the switch 130.

The relay or cutter control magnet 100 shown in FIG. 2 is substituted in the embodiment of FIG. 6 by a resistor 131. Under normal operating conditions, the voltage at the reference point D has the eflfect that a conventional monostable multivibrator 138 switches a transistor 152 to conducting condition so that a capacitor 133 is charged from the voltage across resistor 131 through the transistor 132 and a diode 134. As soon as a voltage pulse is applied to the amplifier input terminals due to the passage of a knot through the sensing gap, this pulse is greatly peaked in a resonance member, composed of capacitors 135 and 136, and a resonance pulse transformer 137. The extremely short pulse of high amplitude is rectified and supplied to the monostable multivibrator 138. Consequently, the transistor 132 as well as the transistor 13? are both blocked as long as the knot pulse persists. When the knot pulse vanishes, the monostable multivibrator 138 triggers to its stable condition and turns the transistor 139 on so that a capacitor 140 is then charged through a diode 141 and the transistor 139 to the voltage across resistor 131 which corresponds to the measurement value of the yarn located immediately behind the travelling knot.

The just-mentioned triggering of the monostable multivibrator 138 also applies energization to a time delay relay 142 through a resistor 143, a capacitor 144 being connected in shunt relation to the relay 142. The period of delay corresponds to the time required for measuring the second yarn distance behind the knot. As soon as the time delay relay 142 switches on, the two capacitors 133 and 140 are abruptly connected by the relay switch 145 to the respective terminals of a resistor 146. If the charging voltage of the capacitors 133 and 140 are equal, which is the case if no double thread is present, then the two voltages compensate each other and no voltage drop occurs at the resistor 146. However, if one of the two capacitors 133 and 140 has received a higher charge than the other because a double thread was located either in front of or behind the knot, then a voltage drop appears along the resistor 146 and is supplied to any suitable amplifier 147.

The amplifier 147 is energized from terminals P and Q connected to a source of voltage. The end stage of the amplifier 147 may be identical with the one shown in FIG. so as to be capable of responding to positive as well as to negative pulses. As mentioned, the polarity of the output voltage is then determined by the one capacitor 133 or 140 which has received the higher charge.

After the controlling amplifier 147 has actuated the cutter control relay or magnet 100a, the multivibrator 138 triggers into its stable starting condition. The capacitors 133 and 146 have meanwhile discharged through the resistor 146. Now the apparatus according to FIG. 6 is ready to perform another measurement. The two diodes 134 and 141 may be silicon p-n junction diodes having a very high blocking resistance. They serve to prevent premature discharge of the capacitors 133 and 140.

It has been described above how multiple yarns preceding or following a knot can be detected by successively sensing and thereafter simultaneously comparing the results. It has been found that with certain kinds of yarn the yarn dimensions, even if no slubs or knots are encountered, may exhibit considerable fluctuations in thickness. Such fluctuations of a normal yarn are not supposed to cause balance disturbances in a comparative measuring operation of the above-mentioned kind. According to another feature of the invention, therefore, it is preferable that the measuring distance of the sensing device is not shorter than a given minimum length so that the signal issuing from the sensing device corresponds to a mean value of the yarn being checked. For example, when the yarn dimension is checked by capacitive means such as are exemplified in FIG. 2b, the capacitor electrodes can have a length corresponding at least to the given minimum length in the travel direction of the yarn. Another way of extending the measuring distance is to have the yarn during each sensing operation travel a given distance through the sensing device such as the capacitors or photocells.

When the occurrence of double threads is to be detected by a sensing device as shown in FIG. 4, for example, the two photocells 101a and 1411b can be spaced from each other a distance corresponding to the desired measuring distance. However, the above-mentioned fluctuations and yarn dimensions may be different for different yarns. In some cases the fluctuations may occur over a relatively short distance, whereas in other cases, the fluctuations may occur over larger distances. It is therefore preferable for the length of the measuring distance to be adjustable. An embodiment as shown in FIG. 6 operates to form a mean value of a yarn cross section, diameter or volume with the aid of the described signal storage system, because the charges stored in the respective capacitors 133 and 140, in fact, constitute the mean values of the single or doubled yarn successively detected. However, simultaneous measuring of the mean value at a single or double yarn would permit dispensing with such a storage system so that the construction and performance of the apparatus is simplified accordingly. The electric circuit connections in the latter case may then correspond to FIG. 2 in conjunction with FIGS. 4 and 5.

An embodiment of the latter type will be described presently with reference to FIGS. 7 and 8.

schematically shown in FIG. 7 at 150 is the knotter of a yarn-package winding machine. A knot X has just been completed by tying the yarn end coming from below to the yarn end coming from the yarn package located above the knotter 150. However the knot is defective because the lower yarn end forms a loop or double yarn. During its travel from the knotter to the package being wound, the yarn travels through two sensing localities 151 and 152 constituted for example by the two photodiodes 191a and 1101b according to FIG. 4. Of course, if desired, two photodiodes may be mounted at each sensing location as explained in the foregoing with reference to the two photodiodes 1010 and 101d shown in FIG. 6, the two diodes being illuminated by two mutually intersecting beams of light at whose intersection point the yarn is located. The measuring locations are placed above the knotter 150 in the yarn path, substantially as described in the above-mentioned copending application Serial No. 398,653, of H. Raasch. In order to mount the two sensors 151 and 152 in accordance with the foregoing description at a sufficiently large distance, for example 10 to 15 cm., therebetween, it would be necessary to provide for a sufliciently large space above the knotter 150. Generally however, the space available in a winding machine above the knotter is not sufficient for such a long measuring distance. It is therefore preferable, according to another feature of the invention, to have the yarn pass laterally in the form of a loop away from and back to the normal path in the manner illustrated in FIG. 7.

The provision of such a loop-shaped yarn path, however, if secured by conventional yarn-guiding means, would increase the yarn tension to such an extent that the yarn would break. It is necessary therefore to construct the yarn guiding means in such a manner that the resulting increase in yarn tension remains negligible. This can be done for example by providing the yarn-deflecting rollers 153, 154 and 155 with ball-bearings which reduce the friction coeflicient from 0.3 to 0.5 down to 0.001 to 0.003. Such small, dust-protected ball-bearings are commercially available.

In this manner the yarn tension can be kept within satisfactory limits despite the deflection of the yarn, particularly since the yarn deflection need be maintained only for a short interval of time subsequent to a knotting operation, for example during an interval of about 1 to 2 seconds. Although for deflection of the yarn over a period of such short duration, the three rollers 153, 154 and 155 must be accelerated each time, the increase in yarn tension resulting from the acceleration can be kept within permissible limits if the rollers and their minute dustsealed ball-bearings are not considerably heavier, for example, than five grams and the outer diameters are not appreciably larger than 7 mm. It may be added that the temporary deflection of the yarn can then be controlled by shifting the roller 154 from the dot-and-dash position 154' to the left hand side of FIG. 7 shortly before the moment when the switch 130 (FIGS. 2, 6) is closed, the closing of this switch being then effected by the same control means, such as a control cam which also controls the operation of the knotter, as is illustrated and described for example in the above-mentioned copending application Serial No. 398,653.

As mentioned, it is of advantage to make the length of the measuring distance variable. This measuring length corresponds to the distance between the entry of the knot into the sensing location 151 and the entry of the knot into the sensing location 152. Since the deflecting roller 154 can be shifted from the inactive position 154, the length of the measuring distance can be varied by extending or shortening the shifting movement of the roller.

FIG. 8 represents the individual stages of operation at which the yarn in the two sensing locations 151 and 152 produce respective signals which are to be compared with each other. The upper diagram shown at a in FIG. 8 relates to a stage in which the knot X has just been tied, as shown in FIG. 7 and the yarn portion above the knot has just been introduced into the sensing or measuring distance by deflection of the guide roller 154. Consequently, at this moment a single yarn passes through both sensing locations 151 and 152 so that the comparison of the corresponding signals does not yield an output signal. The distance travelled by the knot X until it reaches the position shown in diagram of FIG. 8 represents the length l of the measuring distance. During the period of time in which the knot X passes through the measuring distance, a double thread is sensed in the sensing location 151, whereas only a single thread is sensed in location 152. The difference of the corresponding signal voltages is utilized in the above-described manner for stopping the processing of the yarn by severing the yarn.

In diagram d of FIG. 8, it is assumed that the knotting results in the doubling of the upper yarn portion. In this case, two threads of yarn will first pass through the two sensing locations 151 and 152 so that the comparison of the respective sensor signals results in balance. Only after the knot X has passed by the sensing location 151, is a double thread sensed only in the sensing location 152, whereas the sensing location 151 now responds to a single thread. In this case, the measuring distance 1 extends from the exit of measuring location 151 to the exit of measuring location 152 as shown.

It will thus be recognized that by means of an apparatus represented by FIGS. 7 and 8, the sensing operation is performed along a measuring distance which has a given minimum distance in order to determine a mean value of the yarn dimension being checked. The length of the measuring distance can be adjustable if desired. For such purposes, it is of advantage to pass the signal i pulses from the sensors at the sensing locations 151 and 152 through a feedback regulated direct-current amplifier according to FIG. 2 in conjunction with the modifications shown in FIGS. 4 and 5. However, for the purposes of the invention explained with reference to FIGS. 7 and 8, it is not absolutely necessary to employ an amplifier of the type shown in FIG. 2. Other types of amplifiers suitable for static measurements are also applicable. The particular advantage of an apparatus according to FIGS. 7 and 8 resides in the fact that the yarn is simultaneously compared in the two mutually spaced sensing locations 151 and 152 so that the measuring operation is of the comparative and relative type for which the absolute yarn thickness or cross section is not critical. It is therefore not an indispensable requirement to provide for a particularly precise feedback regulation or to make a particularly careful adjustment if the apparatus is used for yarns of respectively different thickness of different cross section.

To those skilled in the art it will be obvious from a study of this disclosure that yarn checking apparatus according to my invention perm ts of various modifications and can be given embodiments other than those particularly illustrated and described herein, without departing from the essential features of the invention and within the scope of the claims annexed hereto.

I claim:

1. Apparatus for checking travelling yarn in textile machinery for slubs, doubling or the like faults, comprising an electrically actuable device for stopping the yarn processing operation, yarn sensing means for issuing signal pulses in response to said faults, a direct current amplifier having an input circuit comprising said sensing means and having an output circuit connected to said device, said input circuit having a fundamental operating voltage upon which said pulses are superimposed, and regulating circuit means connected with said amplifier output circuit for maintaining the voltage of said output circuit substantially constant relative to changes of said fundamental voltage, whereby said device is actuable in response to said yarn-fault responsive signals independently of said changes.

2. Apparatus for checking travelling yarn in textile machinery for slubs, doubling or the like faults, comprising an electrically actuable device for stopping the yarn processing operation, yarn sensing means for issuing signal pulses in response to said faults, a direct-current amplifier having an input circuit comprising said sensing means and having an output circuit connected to said device, said input circuit having a fundamental operating voltage upon which said pulses are superimposed, a negative feedback circuit voltage responsively connected to said output circuit and connected with said input circuit in bucking relation to said fundamental voltage for maintaining the voltage of said output circuit substantially constant relative to changes of said fundamental voltage, whereby said device is actuable in response to said yarnfault responsive signals independently of said changes.

3. Apparatus for checking travelling yarn in textile machinery for slubs, doubling or the like faults, comprising an electrically actuable device for stopping the yarn processing operation, yarn sensing means for issuing signal pulses in response to said faults, a direct-current amplifier having an input circuit comprising said sensing means and having an output circuit connected to said device, said input circuit having a fundamental operating voltage upon which said pulses are superimposed, a feedback circuit connected between said output and input circuits and having means for applying to said input circuit a feedback voltage proportional to the output-circuit voltage and opposed to a proportion of said fundamental voltage, whereby said device is actuable in response to said signals irrespective of changes in fundamental voltage.

4. In yarn checking apparatus according to claim 3, said feedback circuit comprising voltage threshold means so as to apply to said fundamental voltage the proportional share of said output-circuit voltage above a magnitude determined by said threshold'means.

5. Yarn checking apparatus according to claim 3, comprising a Zener diode connected in said feedback circuit for applying said feedback voltage only when said outputcircuit voltage exceeds a threshold value depending upon said diode.

6. In yarn chacking apparatus according to claim 3, said feedback circuit comprising voltage threshold means for applying said feedback voltage only when said output-circuit voltage exceeds a threshold value depending upon said diode, and a reactive impedance member connected in said feedback circuit for storage and delay of the feedback voltage.

7. In yarn checking apparatus according to claim 3, said feedback circuit comprising voltage threshold means for applying said feedback voltage only when said output-circuit voltage exceeds a threshold value depending upon said diode, and an auxiliary amplifier stage interposed between said feedback circuit and said .intput circuit for transferring said feedback voltage to said input voltage.

8. In yarn checking apparatus according to claim 7, said interposed amplifier stage comprising a potentiometric output branch having an adjustable tapped portion connected with said input circuit in series-opposed relation to said fundamental voltage.

9. Yarn checking apparatus according to claim 1, comprising an electromagnet for controlling said device, said magnet having two mutually opposed excitation windings, means for supplying adjustable constant voltage connected to one of said two windings, said output circuit of said amplifier comprising a voltage divider, and said other winding forming part of said voltage divider.

19. In yarn-checking apparatus according to claim 1, said yarn sensing means forming a measuring distance of a given minimum length in the yarn travel direction for response of said sensing means to a mean dimensional value of the yarn.

11. Yarn checking apparatus according to claim 10, comprising adjustable yarn guiding means for varying the length of said measuring distance.

12. In yarn-checking apparatus according to claim 1, said sensing means comprising two sensors spaced from each other along the yarn travel path, and a bridge network having said sensors connected in respective bridge legs and having terminal points for furnishing said sig nal pulse-s.

13. In yarn-checking apparatus according to claim 1, said sensing means comprising a photoelectric device having a photocell whose normal output voltage constitutes said fundamental operating voltage.

14. Apparatus for checking travelling yarn in textile machinery for slubs, doubling or the like faults, comprising an electrically actuable device for stopping the yarn processing operation, photoelectric yarn sensing means having a semiconductor photodiode for issuing signal pulses in response to said faults, said photodiode having a fundamental operating voltage upon which said pulses are superimposed, a direct-current amplifier having an input circuit in which said photodiode is connected, and having an output circuit connected to said device, a feedback circuit connected between said output and input circuits, an auxiliary amplifier stage interposed between said feedback circuit and said input circuit and having a resistive output branch connected in said input circuit in series with said photodiode and poled for mutually opposed polarities of the respective voltage drops of said photodiode and said resistive branch, whereby said device is actuated by said signals irrespective of changes in fundamental voltage.

15. In yarn-checking apparatus according to claim 14, said resistive output branch of said amplifying stage comprising a potentiometer having a variable tapped portion connected in series with said photodiode, and a Zener diode connected in said feedback circuit between said amplifier output circuit and said auxiliary amplifier stage.

References Cited by the Examiner UNITED STATES PATENTS 2,936,511 5/ 1960 Wilson 28-64 3,154,943 11/1964 Garrett et al 2864 X FOREIGN PATENTS 716,370 9/1954 Great Britain.

DONALD W. PARKER, Primary Examiner.

ROBERT R. MACKEY, Examiner.

L. K. RIMRODT, Assistant Examiner. 

1. APPARATUS FOR CHECKING TRAVELLING YARN IN TEXTILE MACHINERY FOR SLUBS, DOUBLING OR THE LIKE FAULTS, COMPRISING AN ELECTRICALLY ACTUABLE DEVICE FOR STOPPING THE YARN PROCESSING OPERATION, YARN SENSING MEANS FOR ISSUING SIGNAL PULSES IN RESPONSE TO SAID FAULTS, A DIRECT CURRENT AMPLIFIER HAVING AN INPUT CIRCUIT COMPRISING SAID SENSING MEANS AND HAVING AN OUTPUT CIRCUIT CONNECTED TO SAID DEVICE, SAID INPUT CIRCUIT HAVING A FUNDAMENTAL OPERATING VOLTAGE UPON WHICH SAID PULSES ARE SUPERIMPOSED, AND REGULATING CIRCUIT MEANS CONNECTED WITH SAID AMPLIFIER OUTPUT CIRCUIT FOR MAINTAINING THE VOLTAGE OF SAID OUTPUT CIRCUIT SUBSTANTIALLY CONSTANT RELATIVE TO CHANGES OF SAID FUNDAMENTAL VOLTAGE, WHEREBY SAID DEVICE IS ACTUABLE IN RESPONSE TO AID YARN-FAULT RESPONSIVE SIGNALS INDEPENDENTLY OF SAID CHANGES. 